Illuminating meaningful diversity in complex feature spaces through adaptive grid-based genetic algorithms

In many fields there exist problems for which multiple solutions of suitably high performance may be found across distinct regions of the search space. Optimisation of the search towards including these distinct solutions is important not only to understanding these spaces but also to avoiding local optima. This is the goal of a type of genetic algorithms called illumination algorithms. In Chapter 2, we demonstrate the use of an illumination algorithm in the exploration of networks sharing only a given set of structural features (valid networks). This method produces a population of valid networks that are more diverse than those produced using state of the art methods, however, it was found to be too inefficient to be usable in real-world problems. Additionally, setting an appropriate resolution of the search requires some amount of prior knowledge of the space of solutions. Addressing this problem is the focus of Chapter 3, in which we develop three extensions to the method: a) an exact method of mutation whereby only valid networks are explored, b) an adaptive mechanism for setting the resolution of the search, c) a principle for tuning mutations parameters to the search’ s resolution. We show that with these additions our method is able to increase the diversity of solutions found in significantly fewer iterations. Finally, in Chapter 4 we expand our method for use in more general problem spaces. We benchmark it against the state of the art. In all tested landscapes, we show that our method is able to identify more meaningful niches in the spaces in the same number of iterations. We conclude by highlighting the limits of our framework and discuss further directions

Using novelty-biased GA to sample diversity in graphs satisfying constraints

The structure of the network underlying many complex systems, whether artificial or natural, plays a significant role in how these systems operate. As a result, much emphasis has been placed on accurately describing networks using network theoretic metrics. When it comes to generating networks with similar properties, however, the set of available techniques and properties that can be controlled for remains limited. Further, whilst it is becoming clear that some of the metrics currently used to control the generation of such networks are not very prescriptive so that networks could potentially exhibit very different higher-order structure within those constraints, network generating algorithms typically produce fairly contrived networks and lack mechanisms by which to systematically explore the space of network solutions. In this paper, we explore the potential of a multi-objective novelty-biased GA to provide a viable alternative to these algorithms. We believe our results provide the first proof of principle that (i) it is possible to use GAs to generate graphs satisfying set levels of key classical graph theoretic properties and (ii) it is possible to generate diverse solutions within these constraints. The paper is only a preliminary step, however, and we identify key avenues for further development

Swimming in nature:A scoping review of the mental health and wellbeing benefits of open water swimming

Purpose: Open water swimming (also known as outdoor or wild swimming) is a popular blue activity which has become of recent interest in the mental health sphere. Moreover, it is an accessible and low-cost activity, requiring little to no specialist equipment other than access to an appropriate blue space. Subsequently, it could be an effective and accessible intervention that supports mental health and wellbeing worldwide. This scoping review aims to summarise the open water swimming literature. Principal methods and results: A comprehensive search, extraction and charting of relevant literature was undertaken, identifying 14 studies exploring the mental health and wellbeing benefits of open water swimming. The findings were synthesised and summarised for both quantitative and qualitative literature, addressing all scoping review aims, whilst also assessing the quality of the literature. Major conclusions: Open water swimming may lead to improvements in mood and wellbeing, reductions in mental distress symptomatology, and was experienced as a positive, enriching process for many. Blue spaces involve embodiment, mindful presence, community and much more, offering for some a therapeutic accretion which sustains mental health and wellbeing across a lifetime. More robust evidence is needed before open water swimming may become a viable mental health resource.</p

A genetic algorithm-based approach to mapping the diversity of networks sharing a given degree distribution and global clustering

The structure of a network plays a key role in the outcome of dynamical processes operating on it. Two prevalent network descriptors are the degree distribution and the global clustering. However, when generating networks with a prescribed degree distribution and global clustering, it has been shown that changes in structural properties other than that controlled for are induced and these changes have been found to alter the outcome of spreading processes on the network. This therefore begs the question of our understanding of the potential diversity of networks sharing a given degree distribution and global clustering. As the space of all possible networks is too large to be systematically explored, a heuristic approach is needed. In our genetic algorithm-based approach, networks are encoded by their subgraph counts from a chosen family of subgraphs. Coverage of the space of possible networks is then maximised by focusing the search through optimising the diversity of counts by the Map-Elite algorithm. We provide preliminary evidence of our approach’s ability to sample from the space of possible networks more widely than some state of the art methods

A comparative study of the efficiency of chart versus computer-generated contrast sensitivity testing in glaucoma patients and controls

Purpose. The goal of this study was to assess the efficiency of chart vs. computergenerated contrast sensitivity tests in glaucoma patients and controls. Methods. A total of 64 individuals (30 young controls, 18 older controls, 16 glaucoma patients) were tested for contrast sensitivity using 4 different tests. Two tests determined contrast sensitivity (CS) for detecting large targets with sharp borders. One of these was the MARS printed chart, and the other a computerized number search test by Bailey. The second assessment determined spatial contrast sensitivity (SCS) for sinusoidal grating targets at several spatial frequencies. One of these was the printed Vistech chart, the other a computerized test by Faubert. Results. Both CS tests showed a decrease in the glaucoma group versus both the control groups (p &lt; 0.001). The tests for SCS demonstrated a decrease in sensitivity both with age (p &lt; 0.001) and in the presence of glaucoma (p &lt; 0.001) across all spatial frequencies. Conclusion. The data indicated that SCS was superior in separating the three study groups. Neither of the computer-generated tests was more sensitive than its printed counterpart

Multilayer distortion in the reconstructed (110) surface of Au

A new LEED intensity analysis of the reconstructed Au(110)-(1×2) surface results in a modification of the missing row model with considerable distortions which are at least three layers deep. The top layer spacing is contracted by about 20%, the second layer exhibits a lateral pairing displacement of 0.07 Å and the third layer is buckled by 0.24 Å. Distortions in deeper layers seem to be probable but have not been considered in this analysis. The inter-atomic distances in the distorted surface region show both an expansion and a contraction compared to the bulk value and range from 5% contraction to about 4% expansion

Laser desorption from and reconstruction on Si(100) surfaces studied by scanning tunneling microscopy

Laser irradiated Si(100) surfaces were studied with an ultrahigh-vacuum scanning tunneling microscopy (STM) system. Our observations indicate that only the dimerized outermost atomic layer is removed if the laser fluence is below the melting threshold with a photon energy larger than the band gap. The newly exposed layer, surprisingly, did not have a dimerized atomic structure, but rather, resembled that of a bulk-terminated structure. The uncovered layer remained atomically smooth (no vacancies) even after 90% of the outermost layer was removed. A possible explanation of these observations is that atom removal occurs by a preferential breakage of the atomic bonds in defect sites. When the laser fluence was increased to levels above the melting threshold, extensive surface roughening occurs